Application program code is often updated, in order to incorporate new features or fix bugs that are identified after the code has been released. However, because patching a software application requires the replacement of program code, it has not been possible to update a running application. Instead, applications must be stopped, and the patch applied to the stored version of the program.
In order to patch running operating systems, various tools have been developed. For example, Avaya Inc. has a system for patching an operating system by implementing a shared library that is mapped in the process address space by the operating system kernel. The assembly code for the system is modified at function entry points to jump to updated functions in a shared library. However, this hot patching capability requires maintaining complex tools for creating the shared library and modifying the assembly code using the operating system kernel. Accordingly, such hot patching implementations are non-portable and proprietary. In addition, they are incapable of hot patching a running application.
The Solaris™ operating system available from Sun Microsystems™ provides some hot patching capability with respect to the operating system. In particular, the operating system is believed capable of unloading and reloading a patched module in a running system, without requiring that the system be rebooted. However, only the operating system kernel or device drivers can be patched using this system. Accordingly, running applications cannot be patched.